Added state machine debug probes to the QDR's "sniffer" OPB slave.

These allow checking the state of various state machines within the OPB
controller, specifically the PHY, the bit align and bit training logic.
This can be useful for figuring out if one of these are stuck in a certain
state which should narrow down problems, for example if sys_clk2x is not
present then bit_train will be stuck at idle.

To check the states read second word of the qdr_ctrl interface. For
example to read the states of QDR0 using Python/corr issue the following
command:

>>> print hex(roach2_10.read_uint('qdr0_ctrl', offset=2))
0xff000130

The two most significant nibbles will be 0xff to show support for this feature.
The three least significant nibbles will be the PHY state, the bit align state,
and the bit train state. In the above example the PHY is stuck in STATE_BIT_ALIGN,
the bit align logic is stuck in STATE_TRAIN, and the bit train logic is stuck in
STATE_IDLE. This indicated that the bit training logic was not clocking.
Added a bit train error probe to the QDR control interface.

The bit train calibration can fail in many ways but only returns a
single bit "cal_fail" signal so it's unclear sometimes _why_ it's
failed. Now you can actually probe the reason calibration has
failed by read the first nibble of qdr_ctrl at offset=3. For
example:

>>> print hex(roach2_10.read_uint('qdr0_ctrl', offset=3))
0xff000001

The 0xff indicates that this feature is supported while the 0x01
means that a "no transition" error has occured. To check what other
error values mean look at qdrc_phy_bit_train.v.
Changed the feature support indicator for the QDR debug probes.

This was a full byte, 0xFF, but has now been set to just one bit 0x80. Software that
wishes to check for support of various features need only read the MSB of the specific
offset for that feature.
Merge remote-tracking branch 'ska-sa/master'
pfb_fir_generic timing fixes

Fanout, especially in asynchronous mode, was causing a simple design to not make timing.
Improvements made, especially in pfb_coeff_gen. Some work still needs to be done in
pfb_fir_taps to reduce en fanout in delay_bram and bus_add blocks.
Merge branch 'master' of http://astro.berkeley.edu/~davidm/mlib_devel